If a point-mass is located at
and is rotating about an
axis-of-rotation
with angular velocity, then the
distance from the rotation axis to the mass is
,
or, in terms of the vector cross product,
. The tangential velocity of the mass is
then , so that the kinetic energy can be expressed as
(cf. Eq.(B.23))

(B.25)

where

In a collection of masses having velocities
, we of
course sum the individual kinetic energies to get the total kinetic
energy.